class_docstr: Each `Instance` in a `Scenario` looks like this:
  
      <input> -> <reference1>
                 <reference2>
                 <reference3> [correct]
                 <reference4>
  
  We can define a label (e.g., letter) for each reference:
  
      <instructions>
  
      <input>                  # train
      A. <reference1>
      B. <reference2>
      C. <reference3>
      D. <reference4>
      Answer: C
  
      <input>                  # test
      A. <reference1>
      B. <reference2>
      C. <reference3>
      D. <reference4>
      Answer:
  
  In general, each example is:
  
      <input_prefix><input><reference_prefixes[0]><reference><output_prefix><output>
docstr:         Example: prefix = "
  A. ", i = 2, return "
  C. "
          
docstr_tok: ["Example",":","prefix","=","``","A",".","``",",","i","=","2",",","return","``","C.","``"]
code: def get_reference_prefix(prefix: str, i: int) -> str:
      """
      Example: prefix = "\nA. ", i = 2, return "\nC. "
      """
      return prefix.replace("A", chr(ord("A") + i))
  
file_path: H2O/h2o_hf/helm/src/helm/benchmark/adaptation/adapters/multiple_choice_joint_adapter.py
imports: from typing import List, Dict, Optional
  from helm.benchmark.adaptation.request_state import RequestState
  from helm.benchmark.scenarios.scenario import Instance
  from helm.common.request import Request
  from .in_context_learning_adapter import InContextLearningAdapter
label_desc: Use image node_id 1 for calling the MultipleChoiceJointAdapter obj's underlying member method code with example usage: obj.get_reference_prefix(prefix, i) and returns: prefix